describing Fe as only something on the inside suggests undeveloped Fe. it's only a one-way street. this is a combination of many factors, 1) that infjs seem to always be the withdrawn types e4, e5, and e9, and 2) infjs almost always seem to have /sp as one of their predominant instinctual energies.
Fe lights up, and if you've never seen an infj light up, you're only getting half the story. true most infjs are quite recessed, cautious, anxious, easily embarrassed, etc, but with enough cajoling you can get them out of their shells.
it's true we spend much time exploring Ni, and in that sense Fe is still in a hypothetical state supported by Ti, more so than it is physically part of our bodies, we may have withdrawn into our own minds almost completely, floating somewhere in the ether. but whenever i am halfway present, people can read my mood quite easily (hence the withdrawing, when negative or unhealthy). this is bc Fe shows its cards when it is active, tangible, and at all open and in-the-moment.
otherwise Fe is just a pressure closing in all around us. a hyper awareness about the emotional climate, the other surrounding us in all forms and guises, and full of a lot of projections based on our interpretation of events, context, social vibe, etc. this is particularly directed to one of the three withdrawn egos, e4, e5, and e9, which define what Fe is principally used for.
i was shitty at this, and i still mostly am in larger social situations, but one on one, i can fit the tenor of the interaction very well, show that i recognize the context of the situation, what the other person feels, interpret their body language, verbal language, etc, can anticipate where they are going, clarify what they think, explore and connect with them in a wide variety of ways, adding a breadth of context and meaning along the way (perspective).
Fe is a great rhetorical skill. it helps us find ways to understand and interpret others, and to craft our own message, communicate in diverse ways, etc. but it needs serious practice. generally speaking, i think entp perspectives on this have been more beneficial for me than anything else.